1. Field of the Invention
The present invention relates generally to communication networks and more particularly to a quality of service agent which optimizes network performance for multimedia communications.
2. Description of the Related Art
It has long been known to provide communication workstations, such as computers and telephones, interconnected by digital communication networks whereby users of the individual workstations may communicate, i.e., transfer information, with one another over the network. In a connection-oriented communication network, the transfer of information between two end-users is accomplished by network functions that select and allocate network resources along an acceptable path. The logical association between the communication end-users is referred to as a call. The chain of associated network resources that support the call is referred to as a connection. Connection management is a network function that is responsible for setting up, maintaining, and taking down connections. Each call request is issued with a set of quality of service (QoS) requirements that govern the resource allocation for the desired connection. Quality of service requirements may include providing access, performance, fault tolerance, and security between a specified set of end systems as directed by the network""s manager.
More recently, users have increasingly requested desktop conferencing, remote presentations, and other multimedia applications between network users. Such multimedia applications have data-intensive sound, voice, and video flows associated therewith. This requires concomitant high bandwidth communication links between distributed computing systems with minimal communication delay, maximum throughput, and instantaneous burst communication capability. The requirements of such multimedia applications accordingly make scheduling appropriate resources to provide for the necessary quality of service very difficult.
To reduce design complexity, most networks are organized as a series of layers, each one built upon its predecessor as described in OSI, A Model for Computer Communications Standards, Black, Ulyess, Prentice Hall, 1991. The number of layers, the name of each layer, contents, and function of each layer differ from network to network. However, in each network, the purpose of the layers is to offer certain services to the higher layers, shielding those layers from the details of how the offered services are actually implemented.
FIG. 1 illustrates a schematic representation of a multi-layered communication network model based on the OSI layered reference model. The lowest layer is the physical layer OSI 1, 20, which is responsible for implementing a physical circuit between data terminal equipment and data circuit terminating equipment. The data link or second layer, OSI 2, 22, is responsible for transfer of data across the link. The third or network layer, OSI 3, 24, specifies the interface of the user into a network and also defines network switching/routing and communications between networks. The fourth or transport layer, OSI 4, 26, provides an interface between the data communications network and the upper three layers. The fifth or session layer, OSI 5, 28, serves as a user interface into the transport layer below, providing a means for exchange of data between users such as simultaneous transmission, alternate transmission, checkpoint procedures and the like. The sixth or presentation layer, OSI 6, 30, ensures that user applications can communicate with each other, and the seventh or application layer, OSI 7, 32, supports the end-user application process.
The fourth layer 26 or transport layer is of particular interest inasmuch as it provides the user options in obtaining certain levels of quality, and is designed to keep the user isolated from some of the physical and functional aspects of the network. To improve network performance, existing techniques rely on transport layer flow control to manage the network performance. However, there are problems with this approach. As multimedia applications become more prevalent, the use of the transport layer as the only mechanism of flow control can result in a reduced network throughput, since the transport layer must handle increased volume of different types of multimedia packets, each with different priorities. Thus, the transport layer mechanism of flow control affects the quality of service for both real time applications, such as voice packets, and non-real time applications, such as data packets, equally from the user""s perspective.
Conventional allocation of network resources is by and large static. A fixed level of quality of service, specified by the user, is matched at connection setup for a call and must be maintained throughout the duration of the call. Static allocation of network resources is inefficient, and typically inadequate for a dynamic networking environment where the user requirements and the quality characteristics of network resources are not static.
Thus, there exists a need for a system and method that addresses the problem of managing network performance which optimizes both end-to-end application performance and network performance.
The present invention provides a unique method and apparatus for a dynamic rate, differential class-based quality of service agent that provides a quality of service guarantee by taking into account the existing state of the network and user-defined classes of service.
In accordance with the present invention, a flexible quality of service agent, separate from the control plane which contains call processing and network management, is provided which optimizes network performance by minimizing the amount of information transmitted over the network to set-up a call and media negotiation, implements admission control to maintain the quality of the ongoing calls and administers the system wide quality of service by providing instantaneous feedback on the current state of the system/network at both the transmitting and receiving end.
These and other advantages and features of the invention will become apparent from the following detailed description of the invention which is provided in connection with the accompanying drawings.